Elliptical exercise device

ABSTRACT

An elliptical exercise device includes a frame supporting guide links which provide for horizontal motion of associated foot support links. A mechanical coupling couples the foot support links to the crank system and intermediate links connect the crank system to the guide links such that a foot receiving area of each foot support link moves in an elliptical path when the crank system rotates.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of U.S. Provisional Application 61/820,312 filed May 7, 2013, the contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to elliptical exercise devices in which the path of travel of a user's foot is generally elliptical.

BACKGROUND OF THE INVENTION

There are a number of exercise devices which operate to allow a user to implement a foot action which follows a generally closed, curved path of travel, simulating running and/or walking. These devices are generally referred to as “elliptical” exercise devices. Many such elliptical exercise devices are large, complicated, costly, and/or have undesirable characteristics related to the motion of the user's feet.

SUMMARY OF THE INVENTION

The present invention offers several embodiments of an elliptical exercise device. Some embodiments offer a path of motion with desirable characteristics. In addition, some embodiments are compact in form and have reduced mechanical complexity.

A first embodiment of an elliptical exercise device includes a frame configured to be supported on a horizontal surface. The frame has a first pivot axis and a second pivot axis defined thereon. A first and a second guide link each have a first and a second attachment point defined thereon. Each guide link is pivotally attached, through its first attachment point, to the frame at the first pivot axis thereof. A first and a second foot link are each configured to support a user's foot thereon. Each foot support link is pivotally connected to the second attachment point of a respective one of the guide links so that when the guide links reciprocate relative to the frame they each cause their respective foot support link to move in a path of travel having a substantially horizontal component of motion. A crank system is pivotally attached to the frame at the second pivot axis thereof. The crank system is rotatable about the second pivot axis. A first and a second mechanical coupling each couple a respective one of the foot support links to the crank system such that rotation of the crank system about the second pivot axis moves the foot support links in a path of travel having a substantially vertical component of motion. Each mechanical coupling includes a foot support portion extending upwardly from a respective one of the foot support links to a fulcrum. Each fulcrum is disposed rearwardly of the first and second pivot axes and above the second pivot axis. A first and a second intermediate link each have a first end connected to the crank system and a second end connected to a respective one of the guide links such that rotation of the crank system about the second pivot axis causes the respective first and second guide links to pivot about the first pivot axis. In operation, a foot receiving area of each foot support link moves in an elliptical path when the crank system rotates about the second pivot axis.

In particular embodiments, each fulcrum is disposed on the frame and in some versions each fulcrum is defined by a pulley rotationally mounted on the frame. Each mechanical coupling may be a flexible element having one end interconnected to the crank system, a second end interconnected to a respective one of the foot support links, and a mid portion extending over one of the fulcrums on the frame. Some versions further include a first and a second forward pulley supported on the frame forwardly of the second pivot axis, with the mid portion of each of the flexible elements further extending over a respective one of the forward pulleys.

In particular embodiments, the intermediate links extend generally vertically. In some versions, each of the guide arms has a connecting portion extending forwardly to a third attachment point and the first end of each of the intermediate links is connected to the third attachment point of a respective one of the guide arms.

In particular embodiments, the foot support portions of the mechanical couplings extend generally vertically when the foot support links are at a middle position.

In particular embodiments, each mechanical coupling includes a rocker arm pivotally interconnected with the frame. The rocker arm has a first end coupled to the crank system and a second end coupled to a respective one of the foot support portions.

In particular embodiments, the foot support links are generally horizontal and the connection between each foot support link and the respective one of the guide links is at a forward end of the support link. The foot receiving area is defined at a rearward end of each foot support link and the foot support portion of each mechanical coupling is connected to a mid portion of a respective one of the foot support links.

In certain embodiments, the guide links have a working length defined between the first attachment point and the second attachment point and the intermediate links have a length that is at least 80% of the guide link working length. In some versions, the intermediate links extend generally vertically.

In particular embodiments, the substantially horizontal component of motion of each foot support link has a higher acceleration when the foot support link is at a forward end of travel than when the foot support link is at a rearward end of travel.

In particular embodiments, each of the guide arms has a third attachment point defined thereon. The first end of each of the intermediate links is connected to the third attachment point of a respective one of the guide arms and the third attachment points are adjustable so as to change a horizontal length of the elliptical path.

In some embodiments, the connection between each mechanical coupling and the crank system is adjustable with respect to the second pivot axis so as to change a vertical height of the elliptical path.

In particular embodiments, the guide links each include hand portions extending upwardly from the first attachment point.

In some embodiments, the crank system has a first and a second crank arm. The first end of each intermediate link is connected to a respective one of the crank arms and each of the mechanical couplings is coupled to a respective one of the crank arms.

In a further embodiment of the present invention, the elliptical exercise device includes a frame configured to be supported on a horizontal surface. The frame has a first pivot axis, a second pivot axis, and a first and second fulcrum defined thereon. Each fulcrum is disposed rearwardly of the first and second pivot axes. A first and a second guide link each have a first and a second attachment point defined thereon. Each guide link is pivotally attached, through its first attachment point, to the frame at the first pivot axis thereof. A first and a second foot support link are each configured to support a user's foot thereupon. Each foot support link is pivotally connected to the second attachment point of a respective one of the guide links so that when the guide links reciprocate relative to the frame, they each cause their respective foot support link to move in a path of travel having a substantially horizontal component of motion. A crank system is pivotally attached to the frame at the second pivot axis thereof. The crank system is rotatable about the second pivot axis. A first and a second flexible coupling each couple a respective one of the foot support links to the crank system such that rotation of the crank system about the second pivot axis moves the foot support links in a path of travel having a substantially vertical component of motion. Each flexible coupling includes a foot support portion extending upwardly from a respective one of the foot support links to a respective one of the fulcrums. A first and a second intermediate link each have a first end connected to the crank system and a second end connected to a respective one of the guide links such that rotation of the crank system about the second pivot axis causes the respective first and second guide links to pivot about the first pivot axis. In operation, a foot receiving area of each foot support link moves in an elliptical path when the crank system rotates about the second pivot axis.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of a first embodiment of an elliptical exercise device in accordance with the present invention;

FIG. 2 is a detailed top view of an embodiment of a crank system for use with some versions of the present invention;

FIG. 3A is a schematic illustrating movement characteristics of a crank-slider mechanism;

FIG. 3B is a schematic similar to FIG. 3A but with a longer connecting arm between the crank and slider; and

FIG. 4 is a side elevational view of a second embodiment of an elliptical exercise device in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be explained with reference to some particular embodiments, and it is to be understood that yet other embodiments, modifications, and variations thereof will be apparent to those of skill in the art in view of the teaching presented herein. As will be clear to those of skill in the art, an elliptical exercise device is designed to be used by a user placing each of their feet on a respective foot receiving area and then moving their feet along a closed elliptical path. As such, an elliptical exercise device includes left and right elements for supporting the respective left and right feet of the user. The right and left components of the exercise device are typically substantially the same, though the machine may be constructed such that the two foot receiving areas are 180 degrees out of phase. That is, when one foot receiving area is moving forwardly, the other foot receiving area is moving rearwardly. The present invention will be described primarily with reference to only one set of the components, with it being understood that the corresponding components on the other half of the device are constructed similarly.

FIG. 1 shows a first embodiment of an elliptical exercise device 10 structured in accord with the principles of the present invention. The device includes a frame 12 which is configured and operative to retain and support the various other components of the device on a horizontal surface such as a floor. The frame 12 is typically fabricated from metal and/or composite materials and/or wood, but any material may be used. The frame 12 has an upper portion 14 and a lower portion 16. The lower portion 16 is configured to contact the horizontal surface while the upper portion 14 supports several components of the device 10. A first pivot axis 18 is defined in a central area of the upper portion 14 of the frame 12. A pair of guide links are pivotally interconnected with the frame so as to be pivotable about the first pivot axis 18.

FIG. 1 is a view of the left side of the exercise device 10 and the left guide link 20 is visible. Because the guide link 20 is shown at the midpoint of its travel, the right guide link is hidden behind it. All left and right components may alternatively be referred to as first and second components for ease of description. The guide link 20 may be said to have a first attachment point 22 towards its upper end and a second attachment point 24 at its lower end. The guide link 20 is pivotally interconnected with the first pivot axis 18 of the frame 12 at its first attachment point 22. In the illustrated embodiment, the guide link 20 further includes a hand portion 26 extending upwardly from the first attachment point 22.

Each guide link 20 has a corresponding foot support link 28 pivotally connected thereto. In the illustrated embodiment, the foot support link 28 has a forward end 30 pivotally interconnected with the second attachment point 24 of the guide link 20. The foot support link 28 further has a foot receiving area 32 defined at its rearward end.

A crank system 34 is pivotally interconnected with the frame 12 such that the crank system 34 rotates about a second pivot axis 36 defined on the frame. In the illustrated embodiment, the crank system is disposed adjacent the lower portion 16 of the frame 12. Referring to FIG. 2, a top view of an embodiment of a crank system 34 for use with some embodiments of the present invention is shown. The crank system 34 includes a first crank arm 38 and a second crank arm 40. As will be described, the guide links and the foot support links are coupled to the crank system 34 such that rotation of the crank system causes the foot receiving areas 32 to move in a closed elliptical path. A flywheel and/or load element 35 may be interconnected with the crank system 34 for creating an exercise load. Such a load element may take the form of an electrical or frictional resistance device, or any other form. Alternatively, a flywheel and/or load element may be integrated into the crank system 34 or connected to the remainder of the device in other ways.

Referring again to FIG. 1, the guide links 20 each include a connecting portion 42 that extends forwardly from the main body of the guide link just below the first attachment point 22. A third attachment point 44 is defined on this connecting portion 42. An intermediate link 46 has a lower, or first, end 48 connected to the outer end of the crank arm 38 and an upper, or second, end 50 connected to the third attachment point 44 of the connecting portion 42 of the guide link 20. As will be clear to those of skill in the art, as the crank system 34 rotates about the second pivot axis 36, the intermediate link 46 will cause the guide link 20 to pivot about the first pivot axis 18. A second intermediate link 52 is also illustrated, connected to the second crank arm 54. It causes corresponding, but out of phase, motion of the other guide link. The third attachment point 44 may be adjustable so as to change a horizontal length of the elliptical path of the foot receiving areas 32. In the illustrated embodiment, a plurality of connecting points 56 are provided on the connecting portion 42 and the third attachment point may be defined at any of these locations.

The elliptical exercise device 10 further includes a first and second mechanical coupling each coupling one of the foot support links to the crank system such that rotation of the crank system about the second pivot axis 36 moves the foot support links 28 in a path of travel having a substantially vertical component of motion. In the embodiment of FIG. 1, the mechanical coupling takes the form of a flexible coupling 60 having a first end 62 coupled to the first crank arm 38 and a second end 64 coupled to the foot support link 28. The second end 64 may be coupled to the foot support link 28 intermediate the forward and rearward ends. In the illustrated embodiment, the second end 64 is coupled to the foot support link close to the rearward end. The area between the forward end and rearward end of the foot support link may be considered a mid portion.

The flexible coupling 60 may be said to have a foot support portion 66 that extends upwardly from the second end 64 to a fulcrum 68. In this embodiment, the fulcrum 68 takes the form of a pulley that is supported on the upper portion 14 of the frame 12, near the rearward end of the upper portion 14. The fulcrum 68 is located rearwardly of the first pivot axis 18 and the second pivot axis 36. As shown, the fulcrum 68 is also above the second pivot axis 36 and on a similar level to the first pivot axis 18. The flexible coupling 60 then extends forwardly from the fulcrum 68 to an upper pulley 70, then downwardly to a forward pulley 72 and then rearwardly to where the first end 62 connects to the crank arm 38. In some embodiments, it is preferred that the flexible coupling 60 extend forwardly from where it connects to the crank system 34 so as to provide the desired motion profile. The flexible coupling may be routed or arranged differently than illustrated in alternative embodiments.

As will be clear to those of skill in the art, as the crank system 34 rotates about the second pivot axis 36, the flexible coupling 60 moves the foot support link 28 upwardly and downwardly, specifically by pivoting the foot support link 28 about the attachment point 24 of the guide link 20. As the crank system 34 rotates about the second pivot axis 36, the flexible coupling 60 and the intermediate link 46 cooperate to cause the foot receiving area 32 of the foot support link to move along a closed elliptical path. This path may be considered to be “fixed” in that the path may not be changed by the user merely applying different forces to the foot receiving areas 32. Unlike some adaptive machines, the user may not vary the stride and length or switch between generally horizontal and vertical motions during use. The profile of the fixed and closed elliptical path may be changed by moving the third attachment point 44 inwardly and outwardly on the connecting portion 42 of the guide link 20. This alters the horizontal stride length of the closed elliptical path. Referring to FIG. 2, the crank aims 38 and 40 may be adjustable in various ways. If the positions of the connections to the flexible coupling and the intermediate links are both changed relative to the second pivot axis 36, the horizontal and vertical motions will be affected. Alternatively, the system may allow for adjustment of the position of the connection of the first end 62 of the flexible coupling 60 to the crank arm 38, thereby allowing a change in the vertical height of the elliptical path. As a further alternative, the position where the second end 64 of the flexible coupling 60 is connected to the foot support link may be moved closer to or farther from the attachment 24. This will change the extent of vertical movement of the foot receiving area 32. Changes to the third attachment point 50, the attachment of second end 64, and/or to the length of or connection to the crank arms may be made by manually adjusting connection points or by various adjustment mechanisms, either manual or powered. In FIG. 1, two exemplary motion paths are indicated at A and B. Other paths may also be provided depending on the configuration and relatively positions of components of the device 10.

An elliptical exercise device may exhibit a variety of paths of foot motion, all of which may be considered to be “elliptical.” Some such elliptical paths are more desirable than others. For example, some paths may be more comfortable or natural feeling to a user. Additionally, the velocity and acceleration of the foot receiving areas at various points along the path of motion will depend on the configuration of the exercise device. Preferred embodiments of the present invention provide a comfortable and natural feeling elliptical path with velocity and acceleration characteristics that provide for a comfortable user experience. In some embodiments, it is preferred that the horizontal component of motion of each foot support link has a higher acceleration when the support link is moving through its forward end of travel than when the foot support link is moving through its rearward end of travel.

FIG. 3A provides a schematic of a crank-slider mechanism to assist in explaining the motion characteristics of some embodiments of the present invention. FIG. 3A shows a circle 80 representing various rotational positions of an end of a crank arm on a crank that rotates about an axis 82. Various rotational positions of the crank are marked as 1-9, with each interval being separated by 22.5 degrees of rotation. A connecting arm 84 is shown connected to the crank 80 at the number 5 position and extends downwardly and forwardly to where it connects with a horizontal line 86. The forward end of the connecting arm 84 may be considered a slider. A crank-slider mechanism operates such that as the crank 80 rotates about the axis 82, the slider, which is connected to the crank 80 by the connecting arm 84, slides back and forth along the line 86. With the crank at position number 5, the connecting arm positions the slider at position 5 on line 86. As the crank 80 rotates clockwise, the slider will move to the right along line 86 until the slider is positioned at position 9 when the crank reaches position 9. As the crank continues to rotate, the slider will move back to position 1 when the crank reaches position 1. The hash marks between positions 1, 5, and 9 on the line 86 indicate the intermediate positions corresponding the locations marked as 2, 3, 4, and 6, 7, 8.

As shown, the hash marks are not evenly spaced along the line 86. Instead, the hash marks are closer to one another near positions 1 and 9. If the crank 80 rotates at a constant speed, the slider will travel at a higher rate of speed at locations where the hash marks are far apart and at lower rates of speed where the hash marks are closer to one another. As will be clear with reference to FIG. 3A, the distance of travel along line 86 is not symmetrical about position 5. Instead, the distance between position 5 and position 9, indicated at 88, is longer than the distance between position 1 and 5, as indicated at 90. As such, the speed of the slider is greater between positions 5 and 9 than it is between positions 1 and 5. A clear difference may also be seen in the distance between the hash mark at location 9 and the next adjacent hash mark versus the distance between the hash mark at position 1 and the next adjacent hash mark. The distance adjacent position 9, indicated at 92, is significantly larger than the distance adjacent position 1, indicated at 94. This means that the slider is moving faster adjacent position 9 than when it is adjacent position 1. An additional characteristic of the motion is that the slider changes directions at positions 1 and 9. As such, the velocity of the slider changes directions. Then, as the slider moves farther away from location 1 or 9, the velocity increases. As such, the rate of acceleration around positions 1 and 9 is greater than around position 5. Because the velocity is greater near position 9, the acceleration is also greater adjacent position 9 than adjacent position 1.

Preferred embodiments of the present invention are arranged such that the rate of acceleration of the foot receiving area is higher when the foot support link is moving through its forward end of travel than when the foot support link is moving through its rearward end of travel. Referring again to FIG. 1, the crank system 34 acts like the crank of FIG. 3A while the upper end 50 of the intermediate link 50 moves similarly to a slider. The motion in 50 is somewhat arcuate, but the characteristics of the motion are the same as discussed for FIG. 3A. That is, when the crank arm 38 is closest to the upper end of its travel, this corresponds to the slider in FIG. 3A being at position 9. This also corresponds to the guide link 20 being at its forward end of travel. As such, the rate of acceleration of the foot receiving area 32, with respect to the horizontal component of motion, is greatest when the foot receiving area is moving through its forward end of travel.

Referring now to FIG. 3B, a schematic of a crank-slider mechanism similar to FIG. 3A is provided. However, this mechanism has a significantly longer connecting arm 96. The longer connecting arm changes the characteristics of the slider travel. Specifically, it reduces the differences between the travel between positions 1 and 5 and the travel between positions 5 and 9. The distance between positions 5 and 9, indicated at 98, is still greater than the distance between positions 1 and 5, indicated at 100. However, the difference between these distances is less than the difference between the distances 88 and 90. Likewise, the difference in velocity, and therefore acceleration, adjacent positions 1 and 9 is less than the configuration in FIG. 3A. The acceleration adjacent position 9 is still greater than the acceleration adjacent position 1, but the differences are reduced. This acts to smooth out the motion of the mechanism. Referring again to FIG. 1, some embodiments are configured so as to maximize the length of the intermediate links 46 and 52, giving a benefit similar to the change between the crank-slider mechanisms of FIGS. 3A and 3B. This positions the crank system 34 adjacent the lower end of the frame 12. In some versions, the length of the intermediate links 46 and 52 is at least 80% of the distance between the first attachment point 22 and second attachment point 24 of the guide links 20. As shown, the intermediate links are also generally vertical in this embodiment.

Referring now to FIG. 4, a second embodiment of an elliptical exercise device in accordance with the present invention is shown at 110. The exercise device 110 shares some components and characteristics with the exercise device 10 in FIG. 1. Only the components that differ will be described. Unlike the device 10 in FIG. 1, the elliptical exercise device 110 includes a mechanical coupling 112 that includes a rocker arm 114 pivotally connected to the frame 116 at pivot location 118. The rocker arm 114 has a forward end 120 that is coupled to the crank system 122 by a flexible element 124. A rearward end 126 of the rocker arm 114 is coupled to the foot support link 128 by a foot support portion 130, taking the form of another flexible element. As the crank system 122 rotates, the flexible element 124 causes the rocker 114 to pivot about the pivot location 118, thereby causing the foot support link 128 to move upwardly and downwardly.

The foregoing describes some particular embodiments of the present invention. Other embodiments, modifications, and variations thereof will be apparent to those of skill in the art in view of the teaching presented herein. The foregoing is not meant to be a limitation upon the practice of the present invention. It is the following claims, which include all equivalents, which define the scope of the invention. 

1-10. (canceled)
 11. An elliptical exercise device comprising: a frame configured to be supported on a horizontal surface, the frame having a first pivot axis and a second pivot axis defined thereon; a first and a second guide link each having a first and a second attachment point defined thereon, each guide link being pivotally attached, through its first attachment point, to the frame at the first pivot axis thereof; a first and a second foot support link each configured to support a user's foot thereupon, each foot support link being pivotally connected to the second attachment point of a respective one of the guide links so that when the guide links reciprocate relative to the frame, they each cause their respective foot support link to move in a path of travel having a substantially horizontal component of motion; a crank system pivotally attached to the frame at the second pivot axis thereof, the crank system being rotatable about the second pivot axis; a first and a second mechanical coupling each coupling a respective one of the foot support links to the crank system such that rotation of the crank system about the second pivot axis moves the foot support links in a path of travel having a substantially vertical component of motion, each mechanical coupling including a foot support portion extending upwardly from a respective one of the foot support links to a fulcrum, each fulcrum being disposed rearwardly of the first and second pivot axes and above the second pivot axis; a first and a second intermediate link each having a first end connected to the crank system and a second end connected to a respective one of the guide links such that rotation of the crank system about the second pivot axis causes the respective first and second guide links to pivot about the first pivot axis; whereby a foot receiving area of each foot support link moves in an elliptical path when the crank system rotates about the second pivot axis.
 12. An exercise device in accordance with claim 11, wherein: each fulcrum is disposed on the frame.
 13. An exercise device in accordance with claim 12, wherein: each fulcrum is defined by a pulley rotationally mounted on the frame.
 14. An exercise device in accordance with claim 12, wherein: each mechanical coupling is a flexible element having one end interconnected to the crank system, a second end interconnected to a respective one of the foot support links, and a midportion extending over one of the fulcrums on the frame.
 15. An exercise device in accordance with claim 14, further comprising a first and a second forward pulley supported on the frame forwardly of the second pivot axis, the midportion of each of the flexible elements further extending over a respective one of the forward pulleys.
 16. An exercise device in accordance with claim 11, wherein: the intermediate links extend generally vertically.
 17. An exercise device in accordance with claim 16, further comprising: each of the guide arms having a connecting portion extending forwardly to a third attachment point; the first end of each of the intermediate links being connected to the third attachment point of a respective one of the guide arms.
 18. An exercise device in accordance with claim 11, wherein: the foot support portions of the mechanical couplings extend generally vertically when the foot support links are at middle position.
 19. An exercise device in accordance with claim 11, wherein: each mechanical coupling includes a rocker arm pivotally interconnected with the frame, the rocker arm having a first end coupled to the crank system and a second end coupled to a respective one of the foot support portions.
 20. An exercise device in accordance with claim 11, wherein: the foot support links are generally horizontal, the connection between each foot support link and a respective one of the guide links being at a forward end of the foot support link, the foot receiving area being defined at a rearward end of each foot support link, and the foot support potion of each mechanical coupling being connected to a mid portion of a respective one of the foot support links.
 21. An exercise device in accordance with claim 11, wherein: the guide links have a working length defined between the first attachment point and the second attachment point; and the intermediate links have a length that is at least 80% of the guide link working length.
 22. An exercise device in accordance with claim 21, wherein: the intermediate links extend generally vertically.
 23. An exercise device in accordance with claim 11, wherein: the substantially horizontal component of motion of each foot support link has a higher acceleration when the foot support link is moving through its forward end of travel than when the foot support link is moving through its rearward end of travel.
 24. An exercise device in accordance with claim 11, wherein: each of the guide arms has a third attachment point defined thereon; the first end of each of the intermediate links being connected to the third attachment point of a respective one of the guide arms; and the third attachment points being adjustable so as to change a horizontal length of the elliptical path.
 25. An exercise device in accordance with claim 11, wherein: the connection between each mechanical coupling and the crank system is adjustable with respect to the second pivot axis so as to change a vertical height of the elliptical path.
 26. An exercise device in accordance with claim 11, wherein: the guide links each include hand portions extending upwardly from the first attachment point.
 27. An exercise device in accordance with claim 11, wherein: the crank system has a first and a second crank arm; the first end of each intermediate link being connected to a respective one of the crank arms; and each of the mechanical couplings being coupled to a respective one of the crank arms.
 28. An exercise device comprising: a frame configured to be supported on a horizontal surface, the frame having a first pivot axis, a second pivot axis, and a first and second fulcrum defined thereon, each fulcrum being disposed rearwardly of the first and second pivot axes; a first and a second guide link each having a first and a second attachment point defined thereon, each guide link being pivotally attached, through its first attachment point, to the frame at the first pivot axis thereof; a first and a second foot support link each configured to support a user's foot thereupon, each foot support link being pivotally connected to the second attachment point of a respective one of the guide links so that when the guide links reciprocate relative to the frame, they each cause their respective foot support link to move in a path of travel having a substantially horizontal component of motion; a crank system pivotally attached to the frame at the second pivot axis thereof, the crank system being rotatable about the second pivot axis; a first and a second flexible coupling each coupling a respective one of the foot support links to the crank system such that rotation of the crank system about the second pivot axis moves the foot support links in a path of travel having a substantially vertical component of motion, each flexible coupling including a foot support portion extending upwardly from a respective one of the foot support links to a respective one of the fulcrums; a first and a second intermediate link each having a first end connected to the crank system and a second end connected to a respective one of the guide links such that rotation of the crank system about the second pivot axis causes the respective first and second guide links to pivot about the first pivot axis; whereby a foot support portion of each foot support link moves in an elliptical path when the crank system rotates about the second pivot axis. 